Impingement cooking ovens of the type disclosed in U.S. Pat. No. 3,884,213 direct jets of temperature controlled gaseous fluids to impinge against irregular shaped food products to subject discrete areas of the surface of the food product to a very high heat transfer rate. The product moves such that areas subjected to the high heat transfer rate move over the surface of the product to obtain desired overall surface effects such as crisping, browning, searing or freezing.
Impingement ovens for foodservice applications enjoy commercial success because the time to cook food products, such as pizza, has been greatly reduced. Ovens used in commercial food processing and bakery applications require that large quantities of food be cooked while minimizing downtime for cleaning, maintenance and repair.
U.S. Pat. Nos. 4,154,861, 4,479,776 and 4,492,839 disclose a variety of fan, plenum and air dispensing devices to precisely control heat transfer to upper and lower surfaces of food products. The food products have been carried on a conveyor through tunnel ovens having air dispensing devices above and below the conveyor for top and bottom heat transfer to the food product.
U.S. Pat. No. 4,474,498 discloses a generally vertically disposed plenum extending along the back wall of an oven compartment, the compartment being divided into a plurality of horizontally spaced chambers and having conveyors moving there-through, one above the other such that a food product is moved through the heating compartment for controlling transfer of heat to the product.
U.S. Pat. No. 4,523,391 disclosed a plenum having a plurality of inwardly inclined front wall panels adapted to direct the flow of air through an elongated plenum outlet port to air dispensing ducts positioned above and below a conveyor. Return ducts and the plenum were formed in a side of the housing adjacent one side of the conveyor permitting the flow of air generally transversely of the conveyor to return to the suction side of the fan.
The apparatus disclosed in the aforementioned patents generally incorporated a blower mounted either above or below a conveyor such that air impinging against the surface of the food product on the opposite side of the conveyor from the blower circulated partially through the conveyor and between air dispensing fingers to return to the intake side of the blower. However, when high air flows are applied to products carried on a solid conveying band, the recirculating air must pass beside the conveyor to return to the intake of the fan.
The air flow rate through ovens of the type hereinbefore described and disclosed in the patents cited above was somewhat limited since air must circulate through the compartment without interfering with air streams which impinge against and transfer heat to the surface of the food product carried by the conveyor. Ovens used for commercial bakery and food processing applications are often equipped with conveyor belts from 8 to 12 feet wide for carrying food products through the oven. Solid impervious conveyor belts and belts constructed of mesh material when completed covered by pans greatly obstruct circulation of air.
The conveyors are generally a flexible band supported by spaced parallel rollers extending across the width of the conveyor. The intense heat in the oven and operating conditions to which conveyor rollers are subjected has heretofore presented maintenance problems. If bearings for supporting the conveyor are mounted outside of the cooking compartment seals are required around shafts projecting through the wall of the chamber. The extension of roller mounting shafts through the wall of the chamber results in heat loss, requires longer support shafts than would be required if bearings were mounted inside the chamber and often interferes with insulating chamber walls. Bearings mounted outside of the chamber often require a secondary oven covering.
If bearings are mounted inside of the cooking compartment, access doors are formed in at least one wall of the cooking compartment to provide access to the interior of the compartment. Multiple access doors are necessary for lubricating, cleaning and replacing bearings supporting the rollers when the support shafts do not extend through oven walls. The doors are expensive, generally used infrequently in bakeries, and are sources of heat loss and mechanical problems.
In ovens used for baking bread, rolls, cookies and other bakery products, vacuum cleaning devices have been employed for removing residue of dough products from the interior of the oven. Further, the access doors were necessary for lubricating, cleaning and replacing bearings supporting the rollers.